Technical Field
Certain embodiments of the present invention relate to a cryocooler and a rotary valve mechanism of a cryocooler.
Description of Related Art
A cryocooler represented by a Gifford-McMahon (GM) cryocooler includes an expander and a compressor of a working gas (also referred to as refrigerant gas). In most cases, the expander includes a displacer which is axially reciprocated by driving means and a regenerator which is built in the displacer. The driving means may have a motor. The displacer is accommodated in a cylinder which guides the reciprocation. A variable volume which is formed between the cylinder and the displacer generated by the relative movement of the displacer with respect to the cylinder is used as an expansion chamber of the working gas. The expander can generate coldness by appropriately synchronizing a volume change and a pressure change of the expansion chamber.
Accordingly, the cryocooler includes a valve portion for controlling the pressure of the expansion chamber. The valve portion is configured so as to alternately switch supply of a high-pressure working gas from the compressor to the expander and recovery of a low-pressure working gas from the expander to the compressor. In general, a rotary valve mechanism is used as the valve portion. The valve portion is also included in other cryocooler such as a pulse tube cryocooler.